ABSTRACT: Search facilities are vital both within folksonomy (or social tagging mechanism) based systems and across folksonomy based systems. Although these systems allow great malleability and adaptability, they also surfer from problems, such as ambiguity in the meaning of tags, flat organisation of tags and some degree of unstabilising factor on consensus about which tags best describe some certain Web resources. It has been argued that folksonomy structure can be enhanced by ontologies; however, as suggested by Hotho et al., a key question remains open: how to exploit the benefits of ontologies without bothering untrained users with its rigidity. In this paper, we propose an approach to address the problem of ambiguity in tagging systems by expanding folksonomy search with ontologies, which is completely transparent to users. Preliminary implementations and evaluations on the efficiency and the usefulness of such expansions are very promising.